The present disclosure relates generally to servo sector data used on devices such as hard disk drives (HDDs). The term “servo sector” (sometimes also referred to as “embedded servo sectors”) describes a pattern of data that is encoded on a device once (e.g., during manufacture) and not re-written thereafter. Servo sectors are relatively small patterns of data arranged at regular intervals along each hard drive tracks comprising variously a preamble field, a digital sync pattern (Servo Address Mark or SAM), digital information for sector and track identification data and analog position burst fields. These tracks are generally configured as concentric circles on magnetic disk(s) of the HDD. While performing tracking and/or data transfer operations, a read/write head detects the servo sectors. A servo demodulator processes the servo sectors, including position burst patterns and sends this information to the servo controller to determine where the read/write head is currently located (e.g., zone, track, data sector) on the disk.
The writing of the servo sectors can be performed under controlled conditions, e.g., during manufacturing. Nonetheless, factors such as component wear, thermal cycling, disk slip, etc., are known to cause errors in the reading of servo sector data during the life of the drive. The controller may have some provisions for dealing with servo sector errors as part of normal operation. However, if there are large number of such errors, it would impact performance, e.g., increasing seek times and data recovery. This may be of greater concern as areal data densities continue to increase. When areal density increases, the servo sectors may be written in smaller areas, which may also result in an increase in servo sector read errors.